According to the ISO standards, a freight container mainly comprises four top corner fittings, four corner posts, four bottom corner fittings, a floor, and a roof, and the auxiliary parts such as side walls, end walls and doors. The top corner fittings are the major weight points upon being lifted with a crane at the container pier or at the container yard. The bottom corner fittings are used for support or fixing a container when the same is mounted on a container trailer, or placed on ground, or on the top of another container. Whenever several containers are piled up one over another, the corner posts of the containers are used to bear the total weight of the containers and goods therein. The goods weight of an individual container is supported with the floor, through which the weight is then equally distributed to the four bottom corner fittings. The roof of a container is mainly used for supporting a container operator to work thereon.
As a result of the aforesaid weight-bearing features, a container must have a strong structure. The aforesaid conventional rigid type of container has met the requirements in terms of a strong structure; however, when an empty container is handled for storage or freight, it will take a considerable space, which means a waste of freight space and cost. Recently, a detachable or foldable container has become a design tendency in the container industry.
A known foldable container substantially has no side walls and roof, but it has two end walls (or end frames) to be foldable to the floor. To form a enclosed type off container, it needs detachable side walls and top board. There is another type of container, of which the side walls are foldable, but its roof has to be removed before being folded up. The extreme of a detachable container is to have the walls, the door, the roof and the floor thereof be able to be assembled together respectively, but the assembling and disassembling operation of such a container always needs a special lifting or assembling equipment, that causes additional costs and manual operation inconveniences.